Propane refining process



'Mamm 5 i914@ Q E, ADAMS PROPANE REFINING PROCESS Filed Dec. 3l, 1936 Patented Mar. 5, 1940 PROPANE REFINING PROCESS Chester E. Adams, Highland, Ind., assignor to Standard Oil Company, Chicago, Ill., a oorporation o! Indiana Application December 31, 1936, Serial No. 118,522

(ci. 19e-73) l, 2A Claims.

This invention relates to refining processes employing propane and it pertains more particf ularly to the refining of hydrocarbon lubricating oils with liquid propane and to methods for re- 5 moving propane from the resulting products.

Propane is being used more and more for the refining of lubricating oils, particularly in processes of deasphalting, deresinating, dewaxing, solvent extraction, acid treating, claying, etc. One of the major problems in all of these processes is the elcient recovery of propane from the resulting products and by-products. Particularly in deasphalting or in the treating of heavy residual stocks, there is a problem of heating the propane mixtures and maintaining emcient heat transferv rates in preheaters and heat exchangers. It appears that there is a tendency for the propane to cause a fouling of the tubes by throwing out resins or other sticky, gummy materials which form an insulating skin on the tube walls. Also, there appears to be a tendency for hot propane mixtures to foam in tubes and ash chambers and to carry entrained oil or asphalt into transfer lines, pumps, storage a@ tanks, etc. An object of my invention is to overcome these dilculties and provide an improved system for heating propane solutions andA recovering propane therefrom.

I have discovered that the capacity'of a commercial deasphalting plant can be markedly increased by my improved heat exchange system, the throughput of the plant being increased in some cases nearly 50%. This is accomplished chiefly by the use of a very simple expedient, the splitting of the propane solution enroute to the flash chamber into two streams, sending one stream directly to the top of the flash chamber to act as a reux and entrainment arrester and passing the other stream through first an ext0 haust steam heater and then a live steam heater,

and introducing this stream into the flash chamn Ihe invention will be described as applied to the treatment of a residual Mid-Continent petroleum stock reduced by noncracking distillation to a viscosity of about 400 seconds Saybolt at 210 F. It should be understood, however, that the invention is equally applicable to the treatment of any residual or distillate stocks as well as the treatment of synthetic oils and oil products, vparticularly products produced by the polymerization of hydrocarbons, the condensation of hydrocarbon radicals with aromatics, products produced by oxidizing, sulfonating, chlorinating or otherwise chemically treating hydrocarbon oils or products, etc. While the invention is described as employing propane, it should be understood that other normally gaseous hydrocarbons may be employed in place thereof, and the term propane is intended to include such hydrocarbons or admixtures thereof with pure propane. In the preferred example I will state conditions for a gas consisting essentially of propane and those skilled in the art will appreciate the necessity and manner-of modifying the conditions when other gases than propane are used.

About 3 to 5 Volumes of propane from storage tank l0 are introduced by pump ll through heater i 2 and line I3 into mixer it wherein the propane is intimately mixed with the residual stock from storage tank l5, steam discharge heater I6, pump ll and line I9. The propane is preferably added to the mixer in stages I9 to avoid entrainment of oil in asphalt particles, i. e., I desire to avoid the agglomeration of insoluble particles prior to the thorough mixture of propane with the stock.

The propane-residuum mixture is then transferred through line' 20 to asphalt settler 2 I, preferably of a temperature of from to 150 F. and a pressure of 390 to 400 pounds gauge. Under these conditions the propane soluble materials separate in an upper layer which is continuously withdrawn through line 22. 'Ihis solution may either be passed through line 23 directly to the propane recovery means, or it may be passed through reducing valve 24, acid mixer 25, sludge settler 26, caustic mixer 21 and caustic settler 28, and line 29. Alternatively, the propane solution may be passed through a propane dewaxing system, a propane-solvent extraction system or other propane refining process.

In the acid treating process I prefer to use about .2 to .3 pound of 93% sulfuric acid per gallon of residual stock charged and I prefer to effect the acid treating and settling at a temperature of about 105 F. and a pressurev of about 210 to 220 pounds gauge. Thesour oil is neutralized incaustic mixer 21 wherein about 0.2 gallon of 2% sodium hydroxide. 'are introduced per gallonof sour oil to be-neutraiized. Acid sludge is withdrawn-from the -base of settler 26 and caustic wash liquid from the base of settler 28, the propane being recoveredrfrom these by-products in a separate recovery system.l

The propane-oil solution from line 23 is rsplit into t'wo streams. About 1,/3 isv passed through line 30 to the upper part of flash tower 3l above bubble plates 32. the original solution, is passed through-line 33, exhaust steam heaterv 34, line 35, live steam heater 36 (steam at about 95 to 100 pounds gauge) and line 31 into the flash towerunderneath the bubble plates. Line 31 may lead into the flash tower ata point above baiile plates 39 or all or a part oi this hot stream may be introduced through line 38 at the'base of the ash tower.

vapor exit temperaturen! about 120 F. and an oil exit temperature of aboutV 275 to 290 F. The oil leaving the exhaust steam heater is rpre1- erably at a temperature of about 260 to 275- F. I

and the oil leaving the live steam heater and entering the flash tower is preferably about Propane from the viiash tower is withdrawn through line 40 to cooling lwater condenser 4i wherein it is liquefied and then returned to propane storage tank I0. Hot oll from the base of the flash tower is withdrawn through line `42 and pressure reducing valve 43 to the upper part of oil stripper 44 'over baille plates 45, so that the hot oil passes in countercurrent contact with steam introduced through line 46. The oil leaves the stripper at a temperature of about 265 to' 270 F. through line 41 which introduces it over plates 4B in dehydrating tower 49. The oil is blown in this tower with air from line 50, thel the asphalt-dash drum is preferably about 315 to 320 F. and since this material has a tendency to foam when flashed at this temperature, I introduce a hot fluxing oil through line 63 at the top of the iiash `tower for breaking this foam. The hot flux oil may be gas oil from line 64 or it may be residual stock from line 65. 4Under the conditions stated I have found it necessary to ern-` ploy about equal volumes of iluxand separated asphalt.

Propane from the top of the asphalt iiash tower is withdrawn through line 66 to high pressure line.40 and propane condenser 4l, thence to storage tank I0. Asphalt from the base of the nash tower is withdrawn at a temperature of about 300 to 310 F. through line 61 and reiucing valve 68 to asphalt stripper 69, wherein 'Lt is stripped with steam from line 10 on baille plates 1I. The stripper operatesat a temperaaioaass j l e f v ture of about 24o' r'., tn'e The other stream, about 3; of s to the base of the o The ash toweris preferably maintainedA at a pressureof 195 to 205 pounds gauge with a l hours. consists in closing the steam heaters oiI from the withdrawn through line 12 to asphalt storage 13 and the propane and steam being withdrawn through line 14, thence through line 54 to steam condenser 55 from which the propane gas is returned to storage as described above.

l The previous methodfor heating the propaneoil solution entering the oil flash tower `was to heat the solution in the exhaust steam heater, introduce the solution at an upper point in the tower and then to use live steam heater 33 as a reboiler, bypassing all 'of the material therethrough and returning the heated oil therefrom il/nash tower. Exhaust steam vheater 34 is commonly referred to as the "preheater and the live steam heater 35 is called the reboi1er. In accordance with my invention I connect the preheater and the reboiler in series andjroute about of the stream through these heaterapassins the otherA third of the solution directly to the top of the flash tower. This process lowers the vapor outlet temperature in the :lash tower from about 22S-250 F. to about 120- 140 F., thus effecting a considerable'saving in the amount of'condensing water necessary for yliquefying thev propane returned to storage for reuse. Since less. propane solution is put through the preheater and the reboiler (heaters 34 and 36) much less steam is required than has heretofore been necessary, and evenwith the increased throughput I have en'ected a saving of from 13 to 18% in steam consumption. The solution introduced through line 30 not only acts vas areux and cooling means, but it arrests entrainment of oil from the dashing step in the lower part of the ilash tower.

Even with my present arrangement of preheater and reboiler in series, I find that with certain stocks the heater tubes are fouled. Cleaning these tubes mechanically is a rather costly job, but I have discovered that these tubes may be cleaned by washing them with hot water. This simple expedient makes it possible to clean the tubes in 'a very short time so that the plant only has to be oil' stream about three or four This water method of cleaning simply rest of the system and' passing hot water through the coils through lines 15. Y

While I have described my invention in detail, it should be understood that I do not limit myself to any of the particular conditions hereinabove set forth except as dened by the following claims which should be construedy as broadly as the prior art will permit. y

I claim:

.1. 'I'he method of removing propane from a solution of propane and deasphalted oil which comprises heating a major part of the deasphalted oil solution to a temperature of about 300 F. and introducing it into a flash zone at a pressure of about 200 pounds per square inch, introducing a minor part of said solution at a temperature of about' 100 F. into the upper part of `said flash zone, whereby it serves as a reux liquid and entrainment arrester, and regulating the size oi.' the major and minor parts of the solution so introduced to obtain a vapor exit temperature oiV about 120 F. and an oil exit temperature of about 290 F.from said flash zone.

2. The method of removing propane from a propane solution of a viscous lubricating oil stock which comprises dividing said solution into minor and major streams, heating the major stream to a temperature of about 300 F. and introducing it stripped asphalt bem: .i

into a flash zone at a pressure of about 200 pounds per square inch, introducing the minor stream at a. temperature of about 100 F. into the upper part of said ash zone whereby it serves as a. reux liquid and entrainment arrester. maint:` .-w; a. flash drum vapor exit tem- 

